Hydrofoil attack craft



June 12, 1956 VAVRA HYDROF'OIL ATTACK CRAFT VAVRA 4 Sheets-Sheet l INVENTOR MICHAEL H.

E82 2380235 mu 2.122%

Filed Oct. 23, 1951 ATTORNEYS June 12, 1956 M, H VAVRA HYDROFOIL ATTACK CRAFT 4 Sheets-Sheet 2 Filed Oct. 23 1951 FIG.3

F I 6. 4. INVENTOR MICHAEL H. VAVRA @wW/K/ Attorneys June 12, 1956 v v 2,749,870

HYDROFOIL ATTACK CRAFT Filed Oct. 25, 1951 4 Sheets-Sheet s F IG. 6.

Walerline as displacement vessel 4 Waterline us hydrofoil vessel INVENTOR ff M4 MICHAEL H. VAVRA MAW 1 J1me 1956 M. H. VAVRA HYDROF'OIL ATTACK CRAFT Filed Oct. 25 1951 4 Sheets-Sheet 4 FIG FIG. IO.

FIG. 9.

INVENTOR MICHAEL H VAVRA ATTORNEYS HYDROFUIL ATTACK CRAFT Michael Hans Vavra, Glen Burnie, Md., assignor to The Hydrofoil Corporation, Washington, D. (3., a corporation of Delaware Application October 23, 1951, Serial No. 252,625

17 Claims. (Cl. 114-665) This invention pertains to marine vessels, and particularly to a novel design of such vessels adapting them for use as landing craft by the armed services.

During the last war, landing boats of various types were used in amphibious and invasion operations, particularly for the lightcring of troops and cargo to invasion beaches. While such craft proved very useful, they were quite cumbersome and slow, and thus presented excellent targets to enemy gunfire, and for prolonged intervals of time. The same lack of speed operated to limit the number of repeated trips that a given vessel could make in a given space of time, thus limiting the speed with which a given landing operation could proceed.

The present invention has for its principal object the provision of an attack craft comparable in size and functions to the above landing vessels, but whose novel features of design and arrangement provide greatly increased speed, thus increasing the load-carrying efliciency and reducing the hazards of enemy gunfire. To this end, the invention utilizes the principles of the hydrofoil, the body of the vessel, after initial speed has been attained, being carried above the water-line upon struts whose lower portions are supported in the water by suitably designed foils. During high speed travel under such conditions, the mtive power derived from gas engines or the like within the hull is transmitted to highly efiicient propeller units located near certain of the underwater foils. Also, provision is made for retracting the struts and foils to positions just beneath, or within the profile of, the hull, and the vessel may then be operated as a conventional waterborne craft, the same propeller units being utilized for propulsive purposes.

Another important advantage of the invention is that it enables a greater degree of stability of the craft as it approaches the landing area, thus providing a relatively stable platform from which offensive firepower can be directed at the beach. This factor, taken in connection with the increase in speed which reduces the time within which the enemy may alter its troop dispositions, makes the vessel considerably safer and more effective than prior landing craft.

Still another object of the invention is to provide an improved design for the supporting foils of the vessel, and a novel combination of special forms of such foils, to achieve great stability and maneuverability.

An additional object of the invention is to provide a hydrofoil vessel in which retractable auxiliary foils, employed to increase the lifting effort at takeoff, can be moved to inoperative positions where they do not impose any aerodynamic drag upon the airborne craft.

The above and other objects and advantages of the invention will best be understood from the following detailed specification of preferred embodiments thereof given by way of example, and taken in connection with the appended drawings, forming a part hereof, in which:

Fig. l is a side elevation, with parts broken away, of one form of attack craft in accordance with the invention,

hired States Patent 0 2,749,870 Patented June 12, 1956 Fig. 2 is a plan view of the same, also with parts broken away, and to a reduced scale,

Fig. 3 is a vertical sectional view taken on line 3-3 of Fig. 2,

Fig. 4 is a vertical sectional view taken on line 44 of Fig. 2, I

Fig. 5 is an enlarged longitudinal section taken through one of the propeler units of the invention,

Fig. 6 is a front elevation of the vessel shown in Figs. 1 to 5,

Fig. 7 is a view showing a modified form of main foil unit,

Fig. 8 is an enlarged sectional view of a modified foil and strut,

Fig. 9 is a section on line 9-? of Fig. 8, and

Fig. 10 a fragmentary section on line ltL-ltl of Fig. 8.

Referring now to the drawings, and especially to Figs. 1 to 4 thereof, there is illustrated an attack craft embodying the invention and in the case selected for illustration having a gross weight of about 6 long tons, and capable of carrying 22 men at a speed of 25 knots when powered by two horsepower engines. The body of this craft, generally designated by reference numeral 19, is preferably formed of a relatively thin shell, and its exterior surfaces are preferably inclined to the vertical to reduce the penetrating power of enemy bullets. The internal framing may be formed of l-beams of some light but strong material, and the under surface of the hull is preferably corrugated for greater stiifness. Skids 12 (see Figs. 3 and 4) are provided along the bottom sides of the hull to protect underlying parts against excessive damage when the vessel is beached.

Before proceeding to a description of the control and propulsive features of the vessel, attention is called to the novel arrangement of exit doors which permits quick disembarkation of the troops with a minimum of exposure. These doors, designated 14, are of a quick-opening type and are located on the forward bulkhead of the main body or cabin of the vessel, and are of sufficient size to permit the troops to emerge, if necessary, without their bodies rising above the silhouette of the vessel. This arrangement, which eliminates climbing over a protective barrier, reduces the probability of casualties. Slits may be provided in these doors for a degree of visibility and to enable enemy fire to be returned.

A raised dome or the like 16, provided with suitable windows and centralized controls, permits greater vision on the part of the pilot of the craft.

The main or principal hydrofoil of this vessel consists, as best shown in Fig. 3 of the drawings, of a center span 18, whoseangle of attack is fixed, and a pair of outer spans 20 and 22, these latter being arranged for independent adjustment about the longitudinal axis of the foil assembly for steering purposes. These adjustable spans act in the manner of ailerons. At the outer end of each of these spans is carried a propeller unit to be described in more detail hereinafter, and designated by reference numerals 24 and 26. The arrangement is such that, while the adjustable foil spans can be controlled independently, the longitudinal or thrust axes of the propeller units remain substantially parallel to the forward direction of travel. Also the propeller units remain in this orientation during retraction of the main foil assembly.

The assembly of main foil units just described, and the propeller units, are connected to the main body of the craft by a pair of struts 28 and 3% these extending into the body and being pivoted as at 32 for movement in a rearward arc until they are received within respective tunnel structures built up into the body of the vessel, these tunnels being arranged as shown at 34 in Fig. 2. When the craft is waterborne, and the foils and propellers completely retracted, the propellers are received within suitable recesses 36 shown in dotted lines in Fig. 1. So positioned, the propellers mean in the water and are available for surface propulsion.

Steering is accomplished by the independent control of the outer foil spans 20 and 22, and when necessary by speed differences in the propeller units; when the main foil assembly is fully retracted, steering is done with 'a conventional rudder 38. I i V The control of the outer foil spans 24 and 22; may be accomplished, for example, by means of a linkage 40 in the nature of a parallelogram, so arranged that when the two outer foils are centralized in preparation for retraction, they will remain level during the retracting movement of the struts ZB and 36, which may be accomplished manually as by a worm 42 operating on a sector gear afiixed to the upper end of each strut which is pivotally mounted as at 32.

Power for the propeller units is provided by a pair of engines 46, 48, each driving as by belts and bevel gears a shaft 50 passing downwardly through the respective struts 28 and 3t) and these in turn driving through bevel gearing a shaft extending through the respective outer foil 26 and 22 to the corresponding propeller unit. It is understood, of course, that reversing gears are provide for reversing the drive mechanism.

The main foil just described carries the main load or weight of the vessel when the latter is operating as a bydro foil craft, but stability necessitates also a forward foil or set of foils, these operating at constant submergence. As best shown in Figs. 1 and 6, the two front foils 52 and 54 are spaced apart laterally of the vessel, and each is of the dihedral type. The foils are supported by retractable struts of which one is designated in Fig. l by numeral 56, and control of the retraction may be manual, as by a worm and sector, or by means of a servo unit under control of the pilot. When retracted, the front foil assemblies are contained within suitable recesses such as indicated by the dotted line position of the foil 54 in Fig. 1.

The waterline indicated in Fig. 6 representing the positions of the front foils 52 and 54 when the craft is operating as a hydrofoil is intersected by the inclined foil surfaces of each of the front foils. In other words, these front foils are of the surface-piercing type, and they may be so designed in order to maintain constant submergence in accordance with well known hydrodynamic design principles. In this way, the front foils operate to stabilize the craft with respect to the rear foils, about both the roll and pitch axes.

About midway of the length of the vehicle, there are provided a pair of auxiliary foils 58 and 66 (Figs. 1 and 4), positioned as near the retractable rear foil as possible without interfering with its functioning. These are pivoted at the underside of the hull as at 62, and operated to their up or down condition by servo piston and cylinder mechanisms 64 and 66, supplied with oil under pressure by a small pump driven by the propelling engines. The purpose of these auxiliary foils is to increase the lift during takeoff (transition from waterborne operation to airborne operation), and/or alternatively to reduce the required takeoff speed and simplify the hull design. They are not used during normal operation in either the airborne or waterborne condition of the vessel. Fig. 4 shows these foils in their fully extended position, and when retracted against the hull they are protected by the skids 12, for example when the vessel is. run upon the beach.

The engines 46 and 48 are or the type in which the cooling system is self-contained, making it unnecessary to provide for intake of the surrounding water as is usually done in such vessels. Each engine is provided with a radiator 68 (Fig. 3) through which cooling air is drawn asbyafan7t). i

The use of two engines provides an efficient' and balanced distribution of weight-and power, but obviously the axis of rotation of the strut or foil.

a single centrally located engine could be used to power one or more propeller units, and it is not intended to limit the invention to the particular power system shown.

While the propeller units have been shown as mounted at. the outer ends of the main foil assembly, it can readily be arranged that these be located at the points of intersection of the struts with the foil assembly. Other modifications are possible in this portion of the structure.

One form of propeller unit is shown to a larger scale in Fig. 5 of the drawings, where numeral '78 designates the outer shell or housing of the unit. Connected to the inside of this shell are stator blades 30, 82 which support bearings for a shaft 84 whose forward end carries the propeller rotor 86 and blades 88. A fairing tl directs water into the annular region containing the turbine type blades 88, the water then passing over the webs 3t), 82 which thus act as stator elements of the turbine. The water leaves the housing through the tailpipe 92, its increased momentum providing the propulsive force which drives the vessel. The rearward end of shaft 84 carries a bevel gear M which meshes with a bevel gear 96 driven by the shaft passing through the corresponding foil span and strut. Inasmuch as it is necessary both for the foil section to rotate about the lower end of the strut and for the strut to rotate about its pivotal connection within the hull, the power shafts are connected at these points by bevel gearing, worm gearing or like angular gearing, with the driven gear disposed on in this way, continuous transmission of power is assured regardless of the pivotal positions of the parts. The structure by which this can be effected will be detailed in figures t scribed below.

in the embodiment of Figs. 1 to 6, the main foil assembly is of a type having a center span (between the struts) which is fixed as to angle of attack with respect to the struts, the outer spans only being adjustable as to angle. In operation, the angle of attack of the span of the rear foil will vary with the mean angle of attack of the forward foil to give stability and trim to the craft. This arrangement can be varied within the scope of the invention; for example, the entire main foil may be functionally integral, and tiltable to adjust the angle of attack, or it may be divided at its center to provide two independently tiltabic foil sections. This last modification is illustrated in 7, in which the foil assembly consists of two adjustable foils 98 and 100, pivotally connected at the center of the total span as by differential coupling 1 32. The power transmitting gears and shafts are again arranged to drive the propeller units m4 and 1% in any adjusted or retracted position of the foils.

Figs. 8, 9 and it) show an embodiment of the strut and foil assembly in which the main foil sections are rigidly secured to one another, the entire foil being tiltably adjusted with respect to the struts. in this form, and since the tilting of different foil sections to achieve steering control is no longer possible, auxiliary vanes or foils in the nature of rudders are provided. One of the two struts (more may be used if desired) is indicated generally by numeral 105, pivoted at its upper end by virtue of the connection of the upper gear case 119 of the strut to a hollow shaft or tube 112 rotatably supported by the hull as in bearings 114. Looking at Fig. 9 of the drawings, this tube 112 extends across the vessel-to'the top of the other strut (not shown), and at its center may be enlarged to provide space for a bevel gear 116 secured to the drive shaft 118 which in this case may be driven from a single, centrally disposed engine. The engine shaft 120 is secured to a bevel gear 122 meshing with gear 116, and enters the tube 112 through a circumferential slot 124 to permit the rotation of tube 112 and hence the retracting movement of the struts connected thereto. A worm wheel 126 in the form of a ring is secured to tube 112 and meshes with a worm 128 which maybe manually or power operated to rotate the tube and hence move the struts for retraction purposes.

The two struts, of which one is shown in Figs. 8 and 9, are of similar construction, so that only one will be described. The cross shaft 118 has secured to its end a bevel gear 138 which is thus coaxial with the tube 112, and this bevel gear meshes with a pinion 132 secured to a shaft 134 passing downward through the strut 108, carrying at its lower end (Fig. 8) a Worm 136 meshing with a worm wheel 138 secured to a shaft 140 running through the foil 142 and carrying a bevel gear for driving the propeller unit in the manner already described in connection with Fig. 5. Suitable couplings, splines or the like are provided to facilitate manufacture and assembly. The lower end of strut N8 thus constitutes a gear case, whose laterally extending journal collars 144 (Fig. 9) act as bearing for the foil itself. As best shown in Fig. 10, this'gear case is in efifect recessed within the leading edge of the foil 142, and the trailing edge at this point is faired out rearwardly as indicated at 146, to provide necessary stiffness. The foil sections may conveniently be bolted together as at 148, so that the entire foil acts as a single structural element.

It is apparent from the above that the foil, as a unit, can swing about the axis of the shaft 140, and to control this movement so that the foil is always directed at the same angle during retraction (but subject to control of its angle of attack as will be described below), there is provided upon the foil adjacent each of the struts a connecting gear 154 to which is pivoted a control rod 152 which as best shown in Fig. 9 is pivoted at its upper end to a bracket 154 nominally fixed to the hull or to one of the walls forming the retraction tunnel. The resulting parallelogram linkage tilts the foil during retraction of the struts, and maintains the angle of attack constant, as shown in dash lines in Fig. 8 indicating the fully retracted condition of the foil.

In order to ensure that the control rod be subject mainly to tension stresses, and hence to give it the greatest strength for a given size, the pivotal axis of the foil which is represented by shaft 140 is disposed farther behind the leading edge of the foil (distance Y) than is the effective center of the lifting force (distance X). Thus, the foil may have its center of lift approximately one-quarter of the chord behind the leading edge of the foil, in which case the pivot axis of the foil may be from 30 to 35% of the chord behind that edge. In this way, compression forces do not occur in the control rod, and it may be made smaller than would otherwise be the case.

in a desi n such as just described, in which the entire main foil pivots as a unit, steering can no longer be obtained by tilting portions thereof. To overcome this difliculty, steering foils such as indicated by numeral 156 may be secured to the control rods 152, and their position controlled for example by rotation of the con-- trol rod itself, or by suitable linkages, not shown. Obviously, if control is exercised by turning the control rods, suitable modification of the end connections thereof will be made, the details thereof being Well within the skill of the Worker in this art.

Other arrangements of the main foil itself, and of the power transmission system, can be utilized. Thus, the main foil may be divided into three independently adjustable sections, each connected to a strut, and the outer sections controlled for steering purposes while the center section remains in a central position except when retraction occurs, when all three foils pivot under control of a parallelogram linkage. The adjustment for varying the angle of attack may take various forms, and in particular this may be accomplished by movement of the point of connection of the upper end of the control rod 152 on a circular are (as indicated by arrows in Fig. 8) centered on the upper pivotal axis running through tube 112. Such adjustment of this point of connection '6 will tilt the foil connected to that control rod one way. or the other. A pin-and-arcuate-slot connection is adaptable for the purpose, or the bracket 154 may be made movable with respect to its support.

There have been illustrated herein arrangements in which a pair of engines power respective propeller units, and in which a single engine may power two propeller unit. Obviously, one or more engines may equally well be arranged to drive a single, centrally disposed propeller unit, and the number of power sources and propeller units may be changed in other combinations.

While the description herein has been directed to the details of certain preferred embodiments in order to teach the practice of the principles disclosed, it should be understood that these details are exemplary only, and that the invention includes other modifications and arrangements falling within the scope of the appended claims.

What is claimed is:

l. A hydrofoil craft comprising a hull, struts depending from said hull at a position rearwardly of the center of gravity of said craft, first hydrofoils carried by said struts, propulsion units carried by said struts, struts depending from said hull at a location adjacent the forward end thereof, surface-piercing hydrofoils can'ied by the last-named struts, and means for selectively retracting all of said hydrofoils and said propulsion units to positions within the general profile of said hull for operation of said craft as a displacement vessel or to extended position below said hull to operate as craft supporting hydrofoils.

2. The structure in accordance with claim 1, including transversely extending auxiliary hydrofoils having inner ends pivoted beneath said hull on an axis parallel to the longitudinal axis of said hull, and means for pivotally moving said auxiliary hydrofoils around their inner ends between positions closely adjacent the bottom of said hull and positions extending downwardly therefrom, to increase the lifting effort on said hull during transition from operation as a displacement vessel to operation as a hydrofoil vessel.

3. A hydrofoil craft comprising a hull, a foil-strut assembly depending from said hull including struts pivoted for movement between positions extending downwardly from said hull and retracted positions substantially parallel to the bottom plane of said hull, wall structures defining downwardly-open tunnels in said hull, means connected to said struts for the selective swinging and positive control of said struts into retracted positions in which they lie within said tunnels, and hydrofoils carried by said struts and completely retractable into said tunnels or to extended position below said hull to operate as craft supporting hydrofoils.

4. In a hydrofoil craft, a hull, a foil-strut assembly depending from said hull, comprising a hydrofoil carried by at least two struts, propeller means supported by said assembly, means for the selective and positive control of swinging said struts to move said hydrofoil assembly and said propeller means from positions disposed beneath said hull to retracted positions in which said parts lie substantially within the profile of said hull, and means interconnecting the hydrofoil assembly and the craft for maintaining the propulsive axis of said propeller means parallel to the longitudinal direction of said hull during retraction of said struts.

5. In a convertible hydrofoil and displacement vessel, a hull, a strut-foil assembly depending from said hull and comprising at least one strut pivoted within said hull and arranged to extend downwardly therefrom during hydrofoil operation, a foil pivoted at the lower end of said strut, at least one propeller unit carried by said strut, an engine in said hull, and power transmitting connections between said engine and said propeller unit, said connections including a shaft housed within one said strut angle gearing for transmitting power to said shaft at the 7 pivotal connection *between said one strut and said'hull to permit continuous delivery of power to said, propeller unit during pivotal movements of said strut, a control rod secured to said foil, means connecting said control rod to said hull, said control rod forming with said strut and foil a parallelogram linkage to tilt the foil during retraction of said strut and thereby maintaining the angle of attack of said foil constant and the axis of said propeller unit substantially horizontal.

6. In a convertible hydrofoil and displacement vessel.

a hull, a strut-foil assembly depending from said hull and including at least one strut, re-entrant tunnel structures extending upwardly into said hull and open downwardly, foil-carrying struts pivoted at the forward ends of said tunnel structures, and means connected to said struts for the selective and positive control in pivoting said struts to move them from positions extending downwardly from and below said hull to positions in which they are received within said tunnel'structures.

. 7. In a convertible hydrofoil and displacement vessel, a hull, spaced struts pivotally carried by said hull and arranged to move selectively between positions in which they extend downwardly from said hull to retracted po sitions in which they are disposed within the profile of said hull, hydrofoil elements supported by said struts at the outer extremities of the latter and extending laterally beyond said struts, propeller units supported at the outer ends of said hydrofoil elements, and means defining downwardly-open recesses in said hull to receive said struts and said propeller units when said struts are moved to their retracted positions.

8. A convertible marine vessel operable selectively as a displacement vessel or a hydrofoil vessel, comprising a hull, retractable hydrofoils carried by said hull, struts connecting said hydrofoils with said hull, propeller units carried by said struts, means for transmitting power from said hull to said propeller units, said means including swivel connections to enable transmission of power continuously during retraction of said hydrofoils and after full retraction thereof, to enable said propellers to drive said vessel in either of said selective conditions, means for maintaining the thrust axes of said propeller units parallel to the axis of said hull in all positions of said struts and said hydrofoils, said means including a control rod operatively connected to said propeller units, means connecting said control rod to said hull, said control rod forming with said struts and propeller units a parallelogram linkage to tilt the propeller units during retraction of said struts.

9. The combination, with a hydrofoil vessel having a hull, of forwardly disposed retractable surface-piercing hydrofoils of the constant submergence type, rearwardly disposed retractable hydrofoils, and means for adjusting the angle of attack of said rearwardly disposed hydrofoils.

10. The combination of claim 9, and intermediate'retractable hydrofoils diverging laterally from the bottom center of said hull at a point between the forward hydrofoils and the rearward hydrofoils.

11. The structure in accordance with claim 5, including means for adjusting the point of connection of said control rod to said hull.

12. The structure in accordance with claim in which said strut is pivotally connected to said hull, and in which the pointof-connection of said control rod to said hull is adjustable about the pivotal connection of said strut to said hull.

- '13. In a hydrofoil vessel, a hull, retractable struts depending from said hull on opposite sides of the vertical center line of said hull, a hydrofoil assembly on each side of said vertical center line connected to the lower extremities of said struts, said hydrofoil assemblies comprising surface-piercing hydrofoils and another retractable hydrofoil assembly spacedrearwardly from the other said assemblies and being angularly adjustable as to angle of attack with respect to the forward direction of said vessel.

14. In a hydrofoil vessel as claimed in claim 13, all of said hydrofoil assemblies being selectively retractable within the general profile of said hull for operation of said craft as a displacement vessel or to extend their position below said bull to operate as craft supporting hydrofoils.

15. In a hydrofoil vessel as claimed in claim 14, said other hydrofoil assembly constituting a fully submerged hydrofoil and including a fixed central foil and a pair of angularly adjustable foils disposed beyond the ends of said central foil.

16. A hydrofoil craft comprising a hull, struts depending from said hull at a position rearwardly of the center of gravity of said craft, first hydrofoils carried by said struts, propulsion units carried by said struts, struts depending from said hull at a location adjacent the forward end thereof, surface piercing hydrofoils carried by the last-named struts, and means for selectively retracting all of said hydrofoils and said propulsion units to po sitions at least as high as the lowermost portion of the bottom of the craft for operation of said craft as a displacement vessel or to extended position below said hull to operate as craft supporting hydrofoils.

17. The combination with a hydrofoil vessel having a hull, of forwardly disposed retractable surface-piercing hydrofoils, rearwardly disposed retractable hydrofoils, means for adjusting the angle of attack of said rearwardly disposed hydrofoils, and intermediate retractable hydrofoils diverging laterally from the bottom center of said hull at a point between the forward hydrofoils and the rearward hydrofoils.

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